1. Field of the Invention
Embodiments of the present invention generally relate to the practice of sidetrack drilling for hydrocarbons. More specifically, this invention pertains to a method of developing a re-entry into a parent wellbore from a lateral wellbore. The present invention also relates to a bottom hole assembly for providing re-entry into a parent wellbore.
2. Description of the Related Art
In recent years, technology has been developed which allows an operator to drill a primary vertical well, and then drill an angled lateral borehole off of the primary well at a chosen depth. Generally, the primary vertical wellbore is first cased with a string of casing and cemented. Then a tool known as a whipstock is positioned in the casing at the depth where deflection is desired. The whipstock is specially configured to divert milling bits and then a drill bit in a desired direction for forming a lateral borehole. This process is sometimes referred to as sidetrack drilling.
FIGS. 1A-1G present sequential steps for one known method of forming a lateral wellbore. FIG. 1A presents a partial cross-sectional view of a wellbore 100. The wellbore 100 in this initial step comprises only a primary wellbore 10. The primary wellbore 10 is an essentially vertically formed wellbore extending downward through the earth formation 30. The primary wellbore, or “parent” wellbore 10, is lined with generally tubular casing 12. A cement column 14 fills an annular area radially between the casing 12 and the earth 30.
An anchoring device 50 such as an anchor-packer has been set in the primary wellbore 10. The packer 50 grippingly engages the surrounding casing 12, enabling the packer 50 to act as an anchor against which tools above it may be urged to activate different tool functions. The illustrative packer 50 of FIG. 1A includes an orientation indicating member 52 secured at its top. The orientation indicating member's 52 orientation is checked by running a tool such as a gyroscope indicator or measuring-while-drilling device into the primary wellbore 10.
A whipstock 40 has also been run into the wellbore 100. The whipstock 40 preferably has a stinger 74 (see FIG. 1F) located at the bottom of the whipstock 40. The stinger engages the orientation indicating member 52 of the packer 50. In one procedure, splined connections between the stinger and the orientation indicating member facilitate correct stinger orientation. The stinger allows a concave face 42 of the whipstock 40 to be oriented so as to direct the milling operation in the proper azimuth. In this way, the whipstock 40 is oriented onto the packer 50 so that the upper concave face 42 is downwardly inclined in a desired direction for milling a window 18 through the casing 12 and for drilling the lateral wellbore 20.
A working string 70 has also been lowered into the wellbore 100. The working string 70 may be coiled tubing, drill collars, or other tubular member. A pilot mill 72 is shown attached to a bottom end of the working string 70. The pilot mill 72 includes blades around a radial body of the mill 72 for engaging and cutting the casing 12. In this respect, the milling bit 72 is lowered into the parent wellbore 10 and urged against the upper face 42 of the whipstock 40, thereby forcing the milling bit 72 to deflect in the desired direction to form a window through the casing 12 and the cement 14.
In one illustrative procedure, the whipstock 40 includes an upper pilot lug 41. The working string 70 lowers the milling bit 72 and the whipstock 40 into the primary wellbore 10 together by means of a temporary connection with the pilot lug 41. FIG. 1A shows a shearable setting stud 43 between the pilot mill 72 and the pilot lug 41. In this way, the need for separate trips for running various tools is avoided.
U.S. Pat. No. 6,112,812 discloses a mill which is releasably secured at the top of the whipstock, e.g. with a shearable setting stud connected to a pilot lug on the whipstock. The mill and whipstock can then be lowered into the wellbore together. Rotation of the string rotates the mill, and causes shearing of the connection with the whipstock. In addition, U.S. Pat. No. 6,695,056 provides methods for single-trip milling and drilling of a window and lateral wellbore. These patents are referred to and incorporated herein in their respective entireties by reference.
FIG. 1B shows a next step in the formation of a lateral wellbore 20, in one embodiment. Here, the milling bit 72 is being urged against the whipstock 40 so as to frictionally engage the surrounding casing 12. Rotation of the string 70 with the pilot mill 72 rotates the mill 72, causing the connection, e.g., a single bolt shear lug (not shown), with the whipstock 40 to be sheared. The mill 72 is moved downwardly while contacting the pilot lug 41 and then the concave face 42. This urges the starting mill 72 into contact with the casing 12. Milling of the casing 12 is achieved by rotating the tool 72 against the inner wall of the casing 12 while at the same time exerting a downward force on the drill string 70 against the concave face 41 of the whipstock 40. In FIG. 1B, the milling bit 72 has breached the surrounding casing 12 of the primary wellbore 10. The milling bit 72 will continue to work against the casing 12 until a window 18 begins to be formed.
It is not uncommon for the operator to deploy a series of milling bits during a window formation operation. FIG. 1C shows that the original milling bit 72 has been removed from the wellbore 10, and that the working string has been again run into the primary wellbore 10, but with a new milling bit 72′ disposed at its end. In addition, a watermelon mill 75 is optionally placed along the working string 70 above the second milling bit 72′. Thus, a fuller window 18 may be formed. The milling bits 72′, 76 are rotated until a window 18 is fully formed in the surrounding casing 12 of the primary wellbore 10. The formed window 18 is commonly elliptical, and is dimensioned to allow a drill bit 78 (seen in FIG. 1D) to then be run through the formed window 18 and engaged with the formation 30. In this way, a new lateral wellbore 20 may be formed.
After the window 18 has been formed, the working string 70 and connected mill 72 are pulled from the primary wellbore 10. Thereafter, the working string 70 is again run into the wellbore 100, but with a drilling assembly. The drilling assembly includes a formation drill bit 78. The drill bit 78 is run into the lateral wellbore 20 for drilling of the formation. FIG. 1D shows this next sequential step in the formation of a lateral wellbore 20.
When the desired length of the lateral wellbore 20 is achieved, a generally tubular liner 28 (seen in FIG. 1G) is inserted into the casing 12. The liner 28 is lowered through the parent wellbore 10, deflected radially outward through the window 18, and positioned appropriately within the lateral wellbore 20. A curvature 45 is formed in the liner 28 at the intersection of the primary wellbore 10 and the lateral wellbore 20.
In one procedure, deflection of the liner 28 into the lateral wellbore 20 is by means of the whipstock 20. This procedure is demonstrated in U.S. Pat. No. 5,803,176, entitled “Sidetracking Operations,” issued in 1998 to William A. Blizzard, Jr. et al. The '176 patent was a continuation-in-part of Ser. No. 642,118 dated May 2, 1996, which in turn was a continuation-in-part of Ser. No. 590,747 dated Jan. 24, 1996. Ser. No. 590,747 issued on Mar. 17, 1998 as U.S. Pat. No. 5,727,629, also to William A. Blizzard, Jr. et al. The '629 patent is entitled “Wellbore Milling Guide and Method.” A softer central core material (not shown) may fill the tubular body of the whipstock 40. In this way, the central core of the whipstock may be drilled out for access to the primary wellbore 10 below the window 18.
In an alternate procedure, a bent joint or hydraulic kick-over joint (not shown) is placed at the bottom of the liner string 28. The joint is biased to exit the window 18 upon reaching the depth of the window 18. This allows the liner 28 to be placed in the wellbore 100 without need of the whipstock 20 (or other deflector). Thus, in more recent procedures the whipstock 20 is pulled before the liner 28 is run into the wellbore 100.
FIG. 1E shows the working string 70 having been pulled from the wellbore 100. A new working string 80 is being lowered into the primary wellbore 10. The working string 80 may be coiled tubing, wireline, or other known string. A fishing hook 82 is disposed at an end of the working string 80. The purpose of the fishing hook 82 is to retrieve the whipstock 40 from the primary wellbore.
FIG. 1F shows the fishing hook 82 engaging the whipstock 40. The whipstock 40 is now being pulled from the packer 50 and attached orientation member 52.
In FIG. 1G it can be seen that the whipstock 40 has been removed from the parent wellbore 10. Where a whipstock is not maintained in the primary wellbore 10, a kick-out sub or other tool (not shown) may be used to urge the liner 28 through the window 18. The liner 28 is placed at the intersection of the parent wellbore 10 and the lateral wellbore 20. The liner 28 may be secured against displacement relative to the casing 12 by a conventional liner hanger, shown at 16. The liner hanger 16 is attached to the liner 28 and grippingly engages the casing 12 of the parent wellbore 10 above the window 18. In the completion of FIG. 1G, the liner 28 is not cemented into place. However, it is understood that the liner 28 may be sealed within the casing 12 of the parent wellbore 10, the earth formation 30, and the lateral wellbore 20 by injecting cement 25 into the liner 28, and then squeezing the cement back upwards into the annular areas surrounding the liner 28. In this way, a cement column is formed around the liner 28.
It may be readily seen that an upper portion of the liner 28 overlaps the casing 12 above the window 18. In this manner, fluid, tools, tubing, and other equipment (not shown) may be conveyed downward from the earth's surface, through an upper portion 6 of the parent wellbore 10, into an upper portion 4 of the liner 28, and thence through the window 18 and into the lateral wellbore 20. The lateral wellbore 20 portion of the subterranean well 100 may, thus, be completed (i.e., perforated, stimulated, gravel packed, etc.).
In the completion of FIG. 1G, the liner 28 includes a slotted liner 27. However, this is purely for purposes of illustration. A solid tubular for later perforation could alternatively be employed. In addition, the liner 28 is preferably cemented into the lateral wellbore 20 by a column of cement 24. In addition, it is understood that other methods of milling a window and forming a lateral wellbore are known. The steps of FIGS. 1A-1G are illustrative, and the methods of the present invention are not limited by the steps taken to form the lateral wellbore or to install a liner 28.
It is known to re-enter the primary wellbore 10 below the window 18 by milling out a portion of the liner 28. U.S. Pat. No. 6,202,752 entitled “Wellbore Milling Methods” discloses one such method. The '752 patent issued to Kuck, et al., in 2001, applies weight to the drill string to cause axial movement during milling. Before that, U.S. Pat. No. 5,803,176 entitled “Sidetracking Operations” was issued. That patent issued to Blizzard, Jr., et al., in 1998. Blizzard, Jr. employed various versions of a mill guide during milling. However, a need yet exists for an improved method that allows the operator to re-enter the primary wellbore from the lateral wellbore. In addition, a need exists for a bottom hole assembly that facilitates re-entry into the primary wellbore.